The etiology of early onset hypercellular obesity is poorly understood. It seems increasingly likely that the metabolic lesion precedes changes in food motivated behavior. A study of the compensatory growth hyperphagia in growing obese Zucker rats and differential response to fasting seen in adult obese Zucker rats should be useful in correlating behavioral alterations and measurable metabolic changes. Data gained from these experiments may be used to develop dietary or behavioral techniques helpful in attenuating the expression of hypercellular obesity. The ability to combine both metabolic parameters and behavioral measurements makes the approach of this proposal particularly versatile and unique.